1. Field of the Invention
The present invention relates to a liquid crystal material showing a smectic ‘A’ phase, a liquid crystal display device, a liquid crystal optical space modulation device, and a liquid crystal shutter using the same.
2. Description of the Related Art
In recent years, an active matrix drive system liquid crystal display (LCD) using a thin film transistor (TFT) has been widely used for the purpose from a small device such as a mobile device to a large equipment such as a large screen television. In the LCD, the response speed of a liquid crystal material has been speeded up by adopting impulse drive system or the like. However, since the response speed of the liquid crystal material itself is fundamentally slow, there is a disadvantage that out-of-focus video or the like is easily generated. Thus, the video display quality of the LCD remains in a state of being inferior to that of a plasma display panel (PDP), a field emission display (FED) and the like.
For attaining high speed response of the LCD, the frame rate has been changed from 60 Hz to 120 Hz or 240 Hz (high frame rate drive). However, though the video display quality of the LCD somewhat surely depends on a drive system factor including the TFT, the video display quality of the LCD essentially depends on response characteristics of the liquid crystal material itself largely. Thus, unless the response characteristics of the liquid crystal material itself are improved, essential resolution is not able to be obtained, resulting in inability to realize high frame rate drive substantially. Therefore, to realize superior video display quality in the LCD, it has been aspired to attain a liquid crystal material capable of realizing high speed response that is able to address high frame rate drive.
As the liquid crystal material capable of realizing high speed response, nematic liquid crystal (flexoelectric effect), ferroelectric liquid crystal, antiferroelectric liquid crystal and the like are known. In recent years, smectic liquid crystal (electroclinic effect of a smectic ‘A’ phase) has been studied.
The electroclinic effect is a phenomenon as follows. In other words, in the case where an electric field is applied to an uniaxially aligned liquid crystal material (liquid crystal molecules) in the smectic ‘A’ phase, the optical axis (long axis) of the liquid crystal molecules is tilted according to the electric field intensity (for example, refer to Physical Review Letters, vol. 38, 1977, p 848, Garpff et al.). In this case, in the case where the liquid crystal material is arranged between two polarizing plates with each polarization direction perpendicular to each other, the transmitted light amount is changed according to the angle (tilt angle) between the optical axis of the polarizing plate and the optical axis of the liquid crystal molecules. The transmitted light amount is expressed by expression T/T0=sin2(2θ)×sin2(πΔnd/λ), where T represents the transmitted light amount, T0 represents an incident light amount, θ represents a tilt angle, Δn represents a double reflex of the liquid crystal material, d represents a thickness of a liquid crystal layer, and λ represents a wavelength of the transmitted light. Based on the expression, in the case where the tilt angle is +/−45 degree, the transmittance becomes the maximum. The correlation between transmittance in retardation (=Δnd) when the tilt angle is the maximum and the tilt angle (degree) is as illustrated in FIG. 4.
Due to the electroclinic effect, the response time of the liquid crystal material becomes from several μs to several tens μs, and thus the response speed thereof becomes largely increased. In this case, since the tilt angle is proportional to the electric field intensity in the range of low field electric intensity, voltage modulation of the transmittance is enabled. Thus, display mode using the electroclinic effect is significantly suitable for the active matrix drive system, and is useful not only for the LCD but also for other optical devices.
However, in the existing liquid crystal material demonstrating the electroclinic effect, the alignment state of liquid crystal molecules is not sufficiently uniform. Thus, in the past, in the LCD using the existing liquid crystal material demonstrating the electroclinic effect, the transmittance has been hardly controlled precisely, and thus sufficient contrast has not been obtained.
Therefore, in the past, to uniform the alignment state of liquid crystal molecules, a technique to apply a large electric field when an isotropic phase is shifted to the smectic ‘A’ phase in the course of decreasing temperature has been adopted (for example, refer to Chem. Mater, 7, 1995, pp. 1397 to 1402, Naciri et al.). However, in the foregoing technique, there are disadvantages that alignment defect easily occur and the procedure is complicated. Further such disadvantages do not result in sufficiently uniform alignment state of the liquid crystal molecules.